The present invention relates to a plunger-operated magnetically actuated reed switch, and particularly to a switch housing permitting mounting such a plunger-operated switch either within a cavity or against a flat surface.
Plunger-operated switches provide simplicity of installation and adjustment for many applications such as in security systems, for monitoring the position of doors and windows, and for controlling electrical circuits in response to the position of elements of industrial machinery.
Mechanically operated switches are subject to loss of reliabilty when used in industrial or outdoor environments where the air carries large amounts of dirt, salt, or oil which can foul the electrical contacts or cause bearings to seize. Magnetically actuated switches such as encapsulated magnetic contact reed switches, on the other hand, are not subject to environmental conditions of those types. Installation of a magnetic contact reed switch for actuation by a magnet carried on a door, window, or moving portion of an industrial machine, may, however, be difficult to accomplish satisfactorily. This may be the case where the switch must operate in response to a precise location of a moving object to meet the purpose at hand, or where there is insufficient space available for mounting a magnet on the moving object.
In some cases it is desirable to have a normally open circuit which closes in response to depression of a plunger, while in other situations the reverse is true.
In either security system or industrial applications, lack of available space, or a desire to protect or conceal a switch, may dictate mounting a switch unit within a cavity. In other situations, it may be required to mount a switch unit against a flat surface, in position to respond to motion of a movable portion of a mechanism in a direction parallel to the flat surface.
Yokoo U.S. Pat. No. 3,260,821 discloses a way of using a magnetic reed switch in a plunger-operated switch unit. Yokoo, however, discloses no particular structure or method for mounting such a switch.
Mayer U.S. Pat. No. 3,243,544 discloses another type of plunger-operated switch utilizing magnetic contact reed switches and movable magnets, but does not disclose a way to mount such a unit other than in a recessed location. The Mayer switch can be set for use in either a normally open or normally closed circuit. Both Yokoo and Mayer, however, require the use of magnets of particular shapes which are unnecessarily expensive to produce and are otherwise undesirably complex in construction.
A roller-operated magnetically actuated switch unit is disclosed in the pending U.S. patent application Ser. No. 207,263, filed Nov. 17, 1980, now U.S. Pat. No. 4,336,518 by Holce, et al. The plunger switch disclosed by Holce, et al. has no provision for alternative mounting locations, being adapted only for recessed mounting, although it can be used in either a normally open or normally closed circuit configuration.
What is desired, then, is a simply constructed plunger-operated magnetically actuated switch unit which can alternatively be operatively installed in an easily prepared cavity, or mounted against a flat surface. Preferably such a switch could be assembled using a single type of magnetic contact reed switch to provide a plunger-operated switch unit having either a normally open or normally closed configuration with the plunger released.